I visited the Mori Museum and it's such a great museum (if you are into modern art especially) and they hold special exihibitions throught the year. This year they had a Weekly Shonen Jump exhibition and it was amazing. Upon finishing the exihibition you are led directly to the souvenir shop; exclusive merchandise available from different animes.

In terms of Kinnikuman you could buy a ton of stuff; I almost bought the S.H Figuarts Kinnikuman exclusive but I stopped myself (this would have been my first S.H Figuarts figure and that would lead me to yet another rabbit hole of collecting).

I was only interested in the Premium Vol. 1 & Premium Vol. 2 Crystal Kinkeshi variant exclusives! I bought two sets (1 to open and one to leave mint).